Things used to be better. It’s an amazingly long standing sentiment regardless of the topic. However we human beings tend to be nostalgic, idealizing our past and forgetting the unpleasant bits. It makes me a little wary whenever someone says "X is worse now".
A recent example is the perception that our congress is more partisan than ever. My initial reaction was that US history is littered with fierce political battles. Ignoring the Civil War (the obvious high water mark of unfriendly politics), is today's congress really more polarized than normal?
I doubted it but, as NPR reported early this year, at least one measurement of congressional roll-call votes showed 2009 as the most contentious year in the Senate since 1953. I liked the idea of exploring roll-call votes to measure tends in partisanship and, thankfully, govtrack.us had great records for both the House and Senate.
After spending way too much time collecting data (57,000 votes!) and inventing a partisanship metric, I'm convinced that the popular perception is right on the money. Voting in the House and Senate really has been getting more polarized. It has steadily increased since the early 1970's.
Moreover, partisanship hasn't been this bad since the beginning of the 20th century, the earliest time I examined.
The Metric
My partisanship measure is nothing fancy. It's simply a number, from 0 to 1, representing how much the Democrats and Republicans disagree. If the two parties completely oppose each other then a vote has a partisanship of 1. If the two parties are indistinguishable, the partisanship is 0.
Take the 2008 House vote on the stimulus as an example. The bill garnered 71.6% of the Democrats and 45.7% of the Republicans. That means there was a difference of 25.9% in the approval rate between the parties. That translates into a partisanship of 0.259, a fairly non-partisan score.
The score for each year is simply the average score of all the contested votes. I consider a vote contested if more than 10% oppose the majority opinion. In other words, I'm looking for the votes that have at least some disagreement and then finding whether the disagreement falls along party lines. I added this condition so that all-to-common fluff votes didn't dilute the average score.
Who's to blame?
Attribution for the shift in the political landscape is beyond the scope of toying around with roll-call votes. Nonetheless I did find some interesting results from measuring the "unity" of each party. The unity score is similar to the partisanship score, but it measures how much a party sticks together on a vote. A unity of 1 means party members all voted the same way. A unity of 0 means they split 50-50.
The unity graph for the senate wasn't terribly interesting. Since the early 1970's both parties become increasingly more unified at roughly the same rate. The unity graph for the House, however, shows periods where one party is clearly more cohesive than the other. Perhaps not much of a surprise, the majority party tends to be the most unified.
What's Up with the 70's?
As far as voting records go, the early 70's look like a bi-partisan nirvana. My best guess is that this is primarily due to two factors. First, the Vietnam War split both parties. It was the major issue of the day and it helped build coalitions across the aisle. Second, the fallout from the civil rights movement led large parts of the South to switch from Democratic to Republican. The rapidly changing constituencies of the two parties may have blurred the regular policy divide.
However it happened, the interactions between the parties have clearly become more polarized. Politics in the US have always been rancorous. But it's rarer for a legislator to break from their party now than anytime in the last century.
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